The invention relates to a method and apparatus for excluding water and other materials for extended periods of time from blast holes in rock. This is particularly useful when blast holes are made but must be left unused for an extended period of time. If water is permitted to seep into the hole, certain blasting agents, such as ammonium nitrate cannot be used. These blasting agents tends to be degraded or otherwise unusable under wet conditions. Water resistant high explosives tend to be considerably more expensive and are therefore less preferred for use under conditions where the less expensive explosives will work.
Heretofore, drilled blast holes have been prepared by drilling rock to depths greater than 100 feet, and charged with cartridge explosives and/or other blasting agents, i.e. ANFO (ammonium nitrate) or NCN (nitro carbon nitrate) where conditions permitted. Certain problems confronted the normal procedure as follows:
After the holes were drilled, they would substantially fill with water or other foreign material via surface conditions, rain or wind, or water seepage in the rock fissures. Also, hydrostatic water pressure would vent through drilled blast holes.
Previous methods used to overcome these problems include pumping or bailing the hole prior to loading with explosives. In most cases, however, the water would seep in too quickly to permit use of water-sensitive blasting agents as an inexpensive explosive charge. Thus, only water-resistant high explosives could be used to overcome these water conditions which, as noted above, caused a substantial cost increase (approximately three times increase in the cost of the blasting agents).
One previous method described in patents to Smith et al., Ser. No. 2,930,276 and to Aitchison et al., Ser. No. 2,745,346, teaches the use of an elongated, inflatable, impervious tube which is first inserted into a hole, inflated with an inert gas, and charged with the liquid oxygen type of blasting material. The prime object of this art was to provide a method of charging blast holes with explosives of the liquid oxygen type. Another claim of these prior art teachings was to solve the water seepage problem during or after charging the explosives, by first inflating the tube and thereby displacing the water prior to charging. While these methods claim to displace water, as will be shown below, they are inadequate to do so or to be effective for an extended period of time. Neither of these references appear to teach that the sleeve will be effective over an extended period of time but rather appear to teach filling the sleeve with appropriate explosives soon after it has been inserted and inflated.